Breaking news today: the essential amino acid L-Tryptophan (TRP) makes people generous! Three psychologists at the University of Leiden, Laura Steenbergen, Roberta Sellara, and Lorenza Colzato, secretly gave 16 participants in an experiment a dose of TRP, solved in a glass of orange juice. The 16 other participants in the study drank plain orange juice, without TRP. The psychologists did not write where the experiment was conducted, but describe the participants as 28 female and 4 male students in southern Europe – which is likely to be Italy, given the names of the second and third authors. Next, the participants were kept busy for 30 minutes with an ‘attentional blink task that requires the detection of two targets in a rapid visual on-screen presentation’. After they had completed a task, they were given a reward of €10. Then the participants were given an opportunity to donate to four charities: Unicef, Amnesty International, Greenpeace, and World Wildlife Fund. And behold the wonders of L-Tryptophan: the 0,8 grams of TRP more than doubled the amount donated from €0.47 (yes, that is less than five percent of the €10 earned) to €1.00. Even though the amount donated is small, the increase due to TRP is huge: +112%.

Why is this good to know? Why does tryptophan increase generosity? Steenbergen, Sellara and Colzato reasoned that TRP influences synthesis of the neurotransmitter serotonin (called 5-HT), which has been found to be associated with charitable giving in several economic experiments. The participants in the experiment were not tested for serotonin levels, but the results are consistent with these previous experiments. The new experiment takes us one step further into the biology of charity, by showing that the intake of food enriched by tryptohan is making female students in Italy more generous to charity.

Tryptophan is an essential amino acid, commonly found in protein-rich foods such as chocolate, eggs, milk, poultry, fish, and spinach. Rense Corten, a former colleague of mine, asked on Twitter: how much spinach the participants would have had to digest to obtain a TRP intake that would make them give an additional €1 to charity? Just for fun I computed this: it is about 438 grams of spinach. Less than the 1161 grams of chocolate it would take to generate the same dose of TRP as the participants got in their orange juice.

The fairly low level of giving in the experiment is somewhat surprising given the overall level of charitable giving in Italy. According to the Gallup World Poll some 62% of Italians made donations to charity in 2011, ranking the country 14th in the world. But wait – Italians eat quite some fish, don’t they? If there is a lot of tryptophan in fish, Italians should be more generous than inhabitants of other countries that consume less fish. Indeed the annual fish consumption per capita in Italy (some 25 kilograms, ranking the country 14th in the world) is much higher than in the Czech Republic (10 kilograms; rank: 50), and the Czech population is less likely to give to charity (31%, rank: 30).

Of course this comparison of just two countries in Europe is not representative of the any part of the world. And yes, it is cherry-picked: an initial comparison with Austria (14 kilograms of fish per year, much less than in Italy) did not yield a result in the same direction (69% gives, more than in Italy). But lining up all countries in the world for which there are data on fish consumption and engagement in charity does yield a positive correlation between the two. Here is the excel file including the data. The relationship is modest (r = .30), but still: we now know that inhabitants of countries that consume more fish per capita are somewhat more likely to give to charity.